1. Field of the Invention
The present invention relates to a data processing apparatus for processing data such as code information and image information and sending the processed data to a printer unit.
2. Related Background Art
Recently, printers such as laser beam printers have rapidly spread far and wide.
The internal structure of a printer is mainly divided, from the standpoint of its function, into a controller unit for performing various controls and a printer unit for actually performing a print process.
The controller unit performs the following processes. Namely, it receives data from a host computer, edits the data into image information (dot information) on the character unit or page unit basis, and outputs to the printer unit the image information together with various print control signals.
The printer unit has a paper feed mechanism and an image forming mechanism such as a semiconductor laser unit, photosensitive drum and the like. The printer unit performs an actual print operation relative to a sheet in accordance with a control signal and image signal sent from the controller unit.
An interface signal group (such as an iamge signal, control signals including command signals and status signals, and other signals) transferred between the controller unit and printer unit is collectively called a video interface signal hereinafter.
With the above-described printer, however, only a single printer unit can be connected to a single controller unit. Therefore, the printer unit cannot have a sufficient operation rate. In addition, each host computer is required to have its dedicated printer unit, which is quite uneconomical. Although the Assignee has various inventions as disclosed in U.S. Pat. Nos. 4,786,923 and 4,682,190 respectively filed on May 20, 1986 and Apr. 30, 1986 and in U.S. patent application Ser. Nos. 947,425 filed on Dec. 29, 1986, No. 942,035 filed on Dec. 15, 1986, No. 291,349 filed on Dec. 29, 1988, No. 025,814 filed on Mar. 13, 1987, and No. 262,350 filed on Oct. 25, 1988. Further improvement has been desired.